THE MEIOTIC BEHAVIOUR OF A NULLI-HAPLOID PLANT IN AVENA SATIVA L.

A nulli-haploid plant (2n = 20) was found in the progeny of an induced monosomic line of Avena sativa L. var. Rodney (2n = 6x = 42). At metaphase 1, the number of associations ranged from 1 to 6 with a mean frequency of 3.5. The pairing frequency can best be explained by the absence of a genetic system, similar to that of chromosome 5B in Triticum aestivum, which would control the diploidisation of hexaploid oats.Chromosomes were associated terminally with an occasional interstitial chiasma. Closed bivalents were rare, and the frequency of trivalent associations was low. This meiotic behaviour confirms the genetic evidence as to the homoeology of the three genomes of the hexaploid oats, but seems to indicate a great deal of structural divergence between them.It is suggested that the long sub-terminal chromosome 7 might carry the gene for diploidisation.

COMPARATIVE GROWTH AND FUNCTION OF NORMAL AND DEFICIENT POLLEN IN A SUBSTITUTION MONOSOMIC OF CHROMOSOME 3D IN WHEAT

Normal pollen with chromosome 3D from Red Bobs had little competitive advantage over pollen deficient for chromosome 3D when a substituted monosomic line of wheat derived from the hybrid Rescue × Golden Ball was selfed. Although the initial rate of pollen tube growth of the 21-chromosome pollen was greater than that of the 20-chromosome pollen, ultimately the two kinds of pollen functioned in the proportions in which they were formed. The 21-chromosome pollen of the substitution monosomic had an advantage over 20-chromosome pollen in a cross with monosomic 3D of Red Bobs, but not with three other 3D monosomic varieties. However, normal pollen in all the reciprocal crosses showed a competitive advantage, affecting fertilization in up to approximately 90% of the cases. Thus chromosome 3D in the Rescue – Golden Ball medium gives the normal pollen little competitive advantage.